1. Field of the Invention
The invention is related to the 3rd Generation Partnership Project (3GPP) radio access network (RAN) standards, high speed uplink packet access (HSUPA) and high speed downlink packet access (HSDPA), and 3GPP Core Network and Speech Codecs and, more particularly, to a system and methods for slow medium access control entity (MAC-e) for autonomous transmission during HSUPA, an for service specific transmission time control in HSUPA.
2. Detailed Description of the Related Art
The Third Generation Partnership Project (3GPP) Technical Specification (TS) 25.309, “Frequency Division Duplex (FDD) Enhanced Uplink; Overall description; Stage 2 TS” has established that some level of enhanced dedicated channel (E-DCH) minimum set support is required to provide backward system compatibility. With a minimum set, autonomous transmission of data packets can occur in an uplink signal without prior allocation of resources by a base station (i.e., Node B) scheduler. In other words, for each user equipment (UE), the minimum set defines a set of transport formats (TFs) for which a valid scheduling grant is not required in order for packets to be transmitted. In normal conditions, the Node B allocates a share of an uplink resource to the UE via a scheduling grant. Only after this allocation of resources occurs is it possible for the UE to transmit packets in the uplink signal. The defined minimum set always guarantees a minimum bit rate, which is typically used for signaling purposes.
From the perspective of the Node B scheduler, the possibility for non-scheduled UEs to autonomously transmit a set of TFs has implications on Node B processing resources, because Node Bs must be continuously ready to process transmissions made from all such UEs, irrespective of the number of UEs that actually perform an autonomous transmission. As a result, the ability of the Node Bs to optimize the use of available Node B processing resources via scheduling becomes limited. Consequently, the complexity of the Node B for processing a given number of TFs may become increased.
The potential for a number of UEs to perform unscheduled autonomous transmissions may require the reservation of a “Rise over Thermal” (RoT) margin for these UEs. In the case of a 2 ms transmission time interval (TTI), a medium access control entity (MAC-e) protocol data unit (PDU) size of 360 bits, and n non-scheduled UEs, the worst case combined data rate in the cell due to autonomous transmission is n*45 kb/sec for a fixed total number of retransmissions of 4. Here, an assumption is made that the 45 kb/sec rate is achieved by transmitting at 180 kb/sec four times, at a reduced power level. With a large number of UEs, the required RoT margin may become significant, which would then degrade the performance of the scheduled transmissions.
The R1-041069 specification, “Signaling Radio Bearer (SRB) Mapping, E-DCH Minimum Set and Node B Complexity Issues”, developed by Motorola, Inc., includes proposed solutions to the foregoing problems, such as restricting the scenarios in which the minimum set applies to cases where, for example, there is no dedicated physical data channel (DPDCH). In the R1-041087 specification, “Autonomous Transmission with Time Division Multiplex (TDM)”, developed by Samsung, the technique disclosed uses a TDM based solution, where autonomous transmissions are only allowed in a subset of TTIs. Another solution proposed in the R1-041211 specification, “Support of Low Minimum Rate for E-DCH”, developed by Lucent Technologies, involves increasing the permitted number of hybrid automatic repeat request (HARQ) transmissions for autonomous transmission rates, or restricting the number of HARQ processes that the UE is permitted to use for autonomous transmissions. However, each of these solutions is less than optimal because they all require a high level of complexity.
The concept of enhanced dedicated channels (E-DCH) support was introduced in 3GPP Rel-6. For an E-DCH transmission, a grant is required, i.e., a non-scheduled grant is required for non-scheduled medium access control dedicated (MAC-d) flows and a serving grant is required for a scheduled transmission. For the scheduled MAC-d data flows, the Node B controls when the UE is allowed to transmit packets and the maximum enhanced dedicated physical data channel (E-DPDCH) to dedicated physical control channel (DPCCH) power ratio that the UE is allowed to use for scheduled data in the following transmission. For the non-scheduled MAC-d flows, the network is permitted to define a maximum number of bits that can be included in a MAC-e PDU for specific MAC-d flows.
In the case of a 2 ms E-DCH TTI, each non-scheduled grant is applicable for the specific set of HARQ processes indicated by radio resource control (RRC), where the RRC can also restrict the set of HARQ processes for which scheduled grants are applicable. Here, the data mapped on non-scheduled MAC-d flows is transmitted as soon as possible by the possible HARQ process restrictions and the possible available power restrictions, with the rate defined by the non-scheduled grant.
The Universal Telecommunication Radio Access Network (UTRAN) is limited in its ability to control the uplink (UL) transmission interval on an E-DCH. The UTRAN can select the TTI to be either 2 ms or 10 ms, when 2 ms TTI is supported by the UE. In the case of a 2 ms TTI, the UTRAN can define the permitted processes for scheduled MAC-d flows and non-scheduled MAC-d flows. Here, it is the base transceiver station (BTS) that decides the scheduling grants of scheduled transmission.
The transmission of a low bit rate service over E-DCH introduces the requirement for large control overhead due to several control channels in the uplink (UL) and the downlink (DL), and because the amount of control bits per TTI is the same for all packet sizes. For example, for each transport block (TB) that is transmitted on an E-DCH, an acknowledge/non-acknowledge (ACK/NACK) is transmitted in the DL and the enhanced transport format combination indicator (E-TFCI), in a robust secure network (RSN), and a ‘Happy bit’ is transmitted in the UL. It is possible to reduce the control overhead by transmitting more packets in the same transport block but less often. However, the payload in the TB and the TTI would be increased.
Preferably, the UTRAN could increase the transmission interval for specific services (e.g. voice over Internet protocol (VoIP)) in the UTRAN in order to increase transmission capacity. Here, the UTRAN should take into account the characteristics of the service, e.g. an assumed or known bit rate, delay requirement, possibly known service data unit (SDU) arrival rates, etc, when defining the transmission interval.
For example, according to rules set forth in chapter 5.1.1. of TS 26.236, in the case of 3GPP adaptive multi-rate (AMR) and AMR-Wideband (WB) codecs in conversational voice over Internet protocol (VoIP) connections, there is one user datagram protocol/real-time transport protocol/Internet protocol (UDP/RTP/IP) packet per speech frame, i.e., one packet in 20 ms. On E-DCH, this leads to a rate of one transport block (TB) transmission per 20 ms because the current MAC specification requires the UE to maximize the throughput of the highest priority data. Speech is typically high priority and thus, MAC tries to send the speech packet as soon as possible when received from the higher layers. However, the service tolerates some additional delay in the radio interface. As a result, the packets could be sent once in every 40 or 60 ms in order to improve transmission capacity. Here, it is possible to assume the additional transmission delay of 20 to 40 ms has an unnoticeable impact in the speech quality.